1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a thin film transistor (TFT) LCD device with a wide viewing angle.
2. Description of Prior Art
In a conventional liquid crystal display, a pair of facing transparent electrodes is respectively formed on each of two substrates, and is used for driving a liquid crystal layer therebetween. In such a device, a displaying means known as a TN (twisted nematic) display is adopted. That is, the liquid crystal display operates by being supplied with an electric field having a direction orthogonal to inner surfaces of the substrates.
However, the TN mode LCD has a narrow viewing angle, which means that the quality of the display greatly depends on the direction of viewing. In order to obtain a wide viewing angle, the IPS type LCD has been developed.
A detailed explanation about operation modes of a typical IPS-LCD device 1 is provided hereinbelow, with reference to FIGS. 7 to 9.
As shown in FIGS. 7–8, upper and lower substrates 11 and 12 are spaced apart from each other, and a liquid crystal layer 17 is provided thererbetween. The substrates 11 and 12 are called a color filter substrate and a TFT substrate, respectively. A multiplicity of pixel and common electrodes 161 and 151 is disposed on the lower substrate 12. The pixel and common electrodes 161 and 151 are parallel to but spaced apart from each other.
When no electric field is provided between the pixel and common electrodes 161 and 151, long axes of liquid crystal molecules in the liquid crystal layer 17 maintain a predetermined angle relative to the pixel and common electrodes 161 and 151. Typically, the angle is 45 degrees, as represented in FIG. 7.
As shown in FIG. 9, when a voltage is applied between the pixel and common electrodes 161 and 151, a horizontal in-plane electric field that is parallel to a surface of the lower substrate 12 is established between the pixel and common electrodes 161 and 151. The liquid crystal molecules are twisted so as to align according to the electric field. That is, the long axes of the liquid crystal molecules are oriented perpendicular to the pixel and common electrodes 161 and 151.
The IPS-LCD device 1 is a conventional single-domain IPS-LCD device. This type of IPS-LCD device has some inherent problems. First, since the pixel and common electrodes 161 and 151 are all oriented in a single direction, the liquid crystal molecules are rotated only in a single direction. This means that an associated display screen exhibits color shift when the display screen is obliquely viewed while displaying white. Second, of the numerous pixel and common electrodes 161 and 151 are both disposed on the surface of the lower substrate 12. A width of so-called teeth and bone portions of the pixel and common electrodes 161 and 151 cannot be less than about 3 to 4 microns. Thus the aperture ratio of each pixel area is reduced.
It is desirable to provide an improved liquid crystal display device which overcomes the above problems.